In wireless communication systems that employ OFDM, a transmitter transmits data to a receiver using many sub-carriers in parallel. The frequencies of the sub-carriers are orthogonal.
Channel estimation in OFDM is usually performed with the aid of known pilot symbols which are sparsely inserted in a stream of data symbols. The attenuation of the pilot symbols is measured and the attenuations of the data symbols in between these pilot symbols are then estimated/interpolated.
Pilot symbols are overhead, and should be as few in number as possible in order to maximize the transmission rate of data symbols. It is desirable that channel estimation in OFDM be as accurate as possible without sacrificing bandwidth.